WAEC Chemistry 2015 Paper

Concept:Hydrogen acts as a reducing agent only for oxides of metals that are less reactive than hydrogen.Explanation:In the electrochemical or reactivity series, hydrogen is placed above copper, mercury, silver, and gold, but below aluminium, magnesium, and sodium.Therefore, hydrogen can remove oxygen from the oxides of metals less reactive than itself, such as $\mathrm{Ag}_2\mathrm{O}$, $\mathrm{CuO}$, $\mathrm{HgO}$, and $\mathrm{Au}_2\mathrm{O}_3$.Oxides of more reactive metals like aluminium oxide ($\mathrm{Al}_2\mathrm{O}_3$), magnesium oxide ($\mathrm{MgO}$), and sodium oxide ($\mathrm{Na}_2\mathrm{O}$) are too stable to be reduced by hydrogen.Among the given options, only silver oxide can be reduced by hydrogen.The reaction can be represented as:$\mathrm{Ag}_2\mathrm{O} + \mathrm{H}_2 \rightarrow 2\mathrm{Ag} + \mathrm{H}_2\mathrm{O}$.Answer:D. Silver oxide